In recent years, lightweight polymeric blast media have replaced agricultural products, such as walnut shells, apricot pits and the like, for use in blast cleaning of sensitive workpieces. The polymeric blast material is more consistent in its cutting qualities, as well as inert to degradation by environmental factors.
Polymeric blast media are relatively expensive and, in general, must be recovered for reuse. The cleanliness of the abrasive material, however, needs to be precisely controlled where the workpieces to be cleaned include surface tolerances that are critical and the integrity of the substrate cannot be compromised.
Where the blast cleaning operation is directed to relatively small articles and workpieces that can be blasted within a confining apparatus, such recovery for reuse is not difficult. However, where the workpiece to be cleaned is of large size, such as an airplane, the blast media must first be recovered from the work site before it can be cleaned and recycled.
After collection of the blast media from the work site, contamination such as paint flakes, corrosion particles and dirt must be separated from the polymeric media. The contaminants include large and fine material about the same weight as the blast media. Also present are fines and dusts that are lighter in weight than the blast media.